BRUSSELS, Sept 24 (Reuters) - A committee of European Union lawmakers on Monday backed new rules to prevent large London-based investment banks from carrying out key activities in the EU after Brexit, unless they set up fully-fledged branches in the bloc.

The new rules, if approved by EU states and by the whole European Parliament in a second vote, would force foreign investment banks to set up branches in the euro zone if they want to perform services such as proprietary trading and underwriting of bonds and other securities in the bloc. (Reporting by Francesco Guarascio, Editing by Gabriela Baczynska)